Stereo speaker arrangement and circuit

ABSTRACT

A sum speaker is placed behind a panelboard opening in an enclosure. Across the front of the opening and normal to the panel is divider means having speaker apertures therethrough. A baffle member at least as wide as the opening extends across the distal edge of the divider means and parallel to the panel board. Difference speakers are positioned on opposite sides of the divider means, facing in opposite directions. The sum speaker produces sound corresponding to the sum of the left and right stereo channels, while the difference speakers produce sound corresponding to the difference between the left and right channels, with the diaphragms of the difference speakers moving simultaneously in the same direction. This is achieved by a matrixing means comprising an autotransformer. The ends of the transformer coil are connected respectively to the ungrounded output terminal of the left and right channel amplifiers respectively. The difference speakers are connected across the ends of the autotransformer. The sum speaker is connected between the transformer centertap and the grounded output terminals of the two amplifiers. In one embodiment the sum speaker panelboard and the divider are vertical. In another embodiment the sum speaker panelboard is horizontal and the divider means comprises four wings positioned as a Greek cross, with different speakers on each of the wings.

United States Patent [451 Jan. 25, 1972 Kuhlow et a1.

[54] STEREO SPEAKER ARRANGEMENT AND CIRCUIT [72] Inventors: Herbert F. Kuhlow, Cleveland, Ohio; James F. Novak, La Grange Park; John F. Henley, Country Club Hills, both of I11.

[73] Assignee: Pemcor,lnc.

[22] Filed: Aug. 6, 1969 [21] Appl. No.: 847,961

[52] U.S.Cl ..l79/lG,179/1E,181/31B [51] Int. Cl ..I 04r 5/02, GlOk 13/00 [58] Field ofSearch ..179/l G, 1 GA, 1 E; 181/31 B [56] References Cited 2 UNITED STATES PATENTS 3,164,676 1/1965 Brunner ....179/1 3,280,258 10/1966 Curtis ..179/1 FOREIGN PATENTS OR APPLICATIONS 939,511 7/1949 Germany ..179/] E Primary Examinerl(athleen H Claffy Assistant Examiner- Douglas W. Olms AttorneyDarbo, Robertson & Vandenburgh 5 7] ABSTRACT A sum speaker is placed behind a panelboard opening in an enclosure. Across the front of the opening and normal to the panel is divider means having speaker apertures therethrough. A baffle member at least as wide as the opening extends across the distal edge of the divider means and parallel to the panel board, Difference speakers are positioned on opposite sides of the divider means, facing in opposite directions. The sum speaker produces sound corresponding to the sum of the left and right stereo channels, while the difference speakers produce sound corresponding to the difference between the left and right channels, with the diaphragms of the difference speakers moving simultaneously in the same direction. This is achieved by a matrixing means comprising an autotransformer. The ends of the transformer coil are connected respectively to the ungrounded output terminal of the left and right channel amplifiers respectively. The difference speakers are connected across the ends of the autotransformer. The sum speaker is connected between the transformer centertap and the grounded output terminals of the two amplifiers. In

- one embodiment the sum speaker panelboard and the divider are vertical. In another embodiment the sum speaker panelboard is horizontal and the divider means comprises four wings positioned as a Greek cross, with different speakers on each ofthe wings.

9 Claims, 6 Drawing Figures PATENTED M425 5?! 772125.? ova/ QT 7 2,11

LEFT

CHANNEL AMPLIFIER RIGHT ChfA NNEL AMPLIFIER 1 I STEREO SPEAKER ARRANGEMENT AND CIRCUIT SUMMARY OF THE INVENTION The present invention relates to a novel, compact and relatively inexpensive apparatus for achieving stereo reproduction of the left and right channel stereo signals.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an embodiment of the invention;

FIG. 2 is a cross section as viewed at line 2-2 of FIG. 1;

FIG. 3 is a schematic diagram of a matrixing system for use with the embodiment of FIGS. 1 and 2;

FIG. 4 is a perspective view of a second embodiment of the invention;

FIG. 5 is a section as viewed at line 55 of FIG. 4; and

FIG. 6 is a schematic diagram of a matrixing system employed in connection with the embodiment of FIGS. 4 and 5.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS The following disclosure is ofiered for public dissemination in return for the grant of a patent. Although it is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements. The claims at the end hereof are intended as the chief aid toward this purpose, as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

The embodiment of FIGS. 1-3 is primarily intended for use against the wall of a room. It can be employed either as an individual unit or as a component in a console which includes other components, e.g., record changer, tuner, television receiver, etcnWhile the best results are obtained when it is standing upright, as illustrated, it does achieve stereophonic results if it is laid on its back and the listener is outwardly from what had been-the original top or bottom. Normally, the openings in the cabinet would be covered with grill cloth (not illustrated) in the usual manner.

This embodiment comprises an enclosure, generally 10, comprising a front panel 11, a top 12, a base 13, a back 14, and sides 15 and 16. The exact construction of this enclosure is conventional and would follow the usual practices that the manufacturer would otherwise follow for use with a particular type of speaker. In some instances the manufacturer will eliminate the back 14, and in other instances the enclosure may or may not be ported. The front panel has an opening 17 positioned in alignmentwith a sum speakengenerally 18, mounted on the front panel. I

The top and bottom 12 and 13 extend forwardly from panel 11. Extending between the overhand of the top and bottom is a divider 21. Divider 21 bisects opening 17, i.e., it intersects the axis of speaker 18. A front baffle member 22 extends across the overhanging top and bottom in contact with the distal edge 21a of divider 21. The width of a baffle member 22, as measured horizontally across the front, is slightly greater than the diameter of opening 17 and, for best results, should be no less than said diameter.

Divider 21 has a pair of apertures 23 and 24 extending therethrough. These apertures are as close as practical to the axis of speaker 18. In the illustrated embodiment they are above and below the axis respectively. In other embodiments they could be at different distances from panel 11, in which case they could both have the axis bisecting the aperture. This latter arrangement is less desirable than the one illustrated because, principally, it requires a deeper overall apparatus configuration. On opposite sides of divider 21 and facing in opposite directions are difference speakers, generally 25 and 26.

Referring particularly to FIG. 3, sum speaker 18 has a diaphragm 28 and a voice coil 29. Difference speaker 25 has a .45. A wire 46 is connected to the ground connections 36 and 39 of the two amplifiers and to one side of voice coil 29. A wire 47 connects the other side of voice coil 29 to centertap 45. The two voice coils 30 and '33 are connected in series by a wire 47. A wire 48 is connected to connection 35 of amplifier 37, connection 43 of autotransformer 42 and the other end of voice coil 30. A wire 49 connects amplifier connection 38, au totransformer connection 44 and the other end of voice coil One of the advantages of the circuit illustrated in FIG. 3 is that'the autotransformer 42 need not be very critical as to its characteristics. It, of course, should have windings sufficient to carry the current for the sum speaker 18. Its impedance should not be less than about 10 times of the total impedance connected across it; in the illustrated embodiment, the total being that of difference speakers 25 and 26. This can be varied somewhat depending upon the lowest frequency which it is desired to obtain from the difference speakers. In an actual embodiment in which the difference speakers 25 and 26 each had a nominal impedance of about 4 ohms (the series arrangemerit being a total of 8 ohms), an autotransformer 42 having a nominal impedance of about 80 ohms was eminently satisfactory. The autotransformer can be extremely small, e.g., onehalf by one-half inches on a core having E and I laminations. It is relatively inexpensive, e.g., well under half a dollar. This is an entirely difi'e'rent situation from that whichwould pertain with respect tomatrixing circuits requiring a transformer.

The matrixing circuit illustrated inFIG. 3 has a number of other advantages over other matrixing arrangements that have been proposed in the past. The cost factors compare very favorably with matrixing arrangements employing dual voice coils. The present arrangement, of course, only requires a single voice coil on each speaker. Another advantage isthat when one channel is not energized, which will occur at intervals in the receipt of normal program material when one microphone picks up little or 'no sound, the other channel operates normally; because the internal impedance of a constant voltage amplifier is near zero, the inactive amplifier channel acts as a short circuit across that part ofthe system. A common ground is provided for both amplifiers.

There will not be unbalances between the speaker reproductions at different frequencies. This can be a problem with bridge-type matrixing circuits. In bridge-type matrixing circuits, it generally is necessary to have all of the speakers closely matched as to characteristics. This can be difficult with different size speakers, i.e., where the sum speaker is relatively large to obtain effective air coupling for low-frequency reproduction, and the difierence speakers are comparatively smaller, primarily for cost control considerations. In the illustrated circuit the two difference speakers are matched as com-,

pared to each other, but they need not be matched as com- A pared to the sum speaker.

This matrixing circuitcan be employed with two or more sum speakers. In 7 that event, the sum speakers should be matched to each other. They would be connected in series or in parallel between center tap 45 and wire 46. Similarly, while the drawing illustrates a series connection of the difference speakers 25 and 26, these speakers could be connected in parallel. The speakers all should be of the full range type for best results.

The impedance of the speaker arrangement (the speakers plus the matrixing circuit) as seen by the amplifiers at the output terminals thereof will be substantially equal to the impedance of the sum speaker (of speakers) connected between centertap 45 and wire 46. Thus, for example, with sum cuit of FIG. 3 apply equally well to the matrixing circuit of FIG. 6.

The speakers and 26 are so connected (in relation to their position on divider 21) that any given signal applied thereacross causes the diaphragms of the two speakers to move simultaneously in the same direction. That is, as one diaphragm moves in the other moves out.

It is well known that below about 200 cycles there is substantially no directional effect to the sound produced. Above that, for various reasons, the directional effect of the sound waves becomes increasingly more pronounced. With the embodiment illustrated, the lower frequencies that are produced emanate to a greater extent from the sum speaker 18 due to its greater size, the fact that a tuned enclosure is employed in conjunction with it, and the effect of the matrixing circuit on the low-frequency reproduction of the difference speakers. However, a listener, positioned in front of the reproduction apparatus of FIG. 1 (when in position in the average house room having a music reproduction system) will have the definite sensation of stereo reproduction. The front enclosure member 22 can be dispensed with, but its use definitely enhances the stereo effect. Furthermore, it appears that a listener can move farther into the side quadrant (toward one side or other of the cabinet) before the stereo effect is lost.

In the embodiment illustrated in FIGS. 4 through 6, there is an enclosure, generally 55, comprising four sides 56, 57, 58 and 59, a bottom 60 and a sum speaker panel 61. The enclosure stands off the floor on feet 62. The bottom 60 has a port 63. Panel 61 has a speaker opening 64.

Mounted on the top of panel 61 is divider means comprising four wings 66-69 positioned in the form of a Greek cross. The center of the cross is aligned with the axis of the sum speaker, generally 70. A baffle member 71 is affixed to the distal edges of the wings 66-69.

The enclosure 55 is tuned for the particular sum speaker 70 employed. Speaker 70 has a voice coil 74 and a diaphragm 75. Two pairs of smaller difference speakers are employed. Each speaker of a pair being oriented 180 from the other speaker of the pair. One pair is oriented 90 from the other pair. One pair comprises speakers generally 76 and 77. The other pair comprises speakers 78 and 79. Speakers 76-79 have voice coils 82-85 respectively, and diaphragms 86-89 respectively.

The left channel amplifier 37 has output terminals and 36, while the right channel amplifier has output terminals 38 and 39. The autotransformer 42 has two end connections 43 and 44 on its winding, and a centertap 45. A wire 91 connects voice coils 84 and 85 in series. Similarly, voice coils 82 and 83 are connected in series by a wire 92. A wire 93 connects output terminal 35 to autotransformer connection 43, voice coil 82 and voice coil 84. Wire 94 connects output terminal 38, connection 44 of the autotransformer and voice coils 83 and 85. A wire 95 connects centertap to voice coil 74. A wire 96 connects the grounded terminals 36and 39 of the two amplifiers to voice coil 94.

The connections are such that diaphragms 88 and 89 (when considered in relation to their positioning) move in the same direction with a given signal applied thereto. Likewise, diaphragms 86 and 87 always move in the same direction with a given signal. That is, one diaphragm of a pair of speakers will move outwardly at the same time that the other moves inwardly, but this is the same direction since the two speakers of the pair are reversed from one another.

With the arrangement illustrated in FIGS. 4 and 5, and with the overall speaker apparatus positioned near the center of a listening area, one may move to almost any angular position about the apparatus and still obtain a significant stereo listening effect. This-stereo effect is, of course, due to the positioning of the difference speakers 76-79. The sum speaker 70 has a greater low-frequency sound-reproducing effect, but the lower frequencies have little effect on the stereo listening result.

We claim:

1. In a stereo-reproducing apparatus for use with a left channel signal and a right channel signal, the combination comprising: 1

a housing having an approximately vertical front panel board with a speaker opening therein;

a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately horizontal;

a divider mounted in front of said panel board and in juxtaposition thereto, said divider being substantially vertical, substantially normal to said panelboard and coplanar with said axis, said divider having a pair of apertures therethrough;

a first difference speaker mounted on said divider in alignment with one aperture;

a second difference speaker mounted on said divider in alignment with the other aperture;

said difference speakers having diaphragms facing in opposite directions from each other, said difference speakers being positioned as closely adjacent as practical, considering the overall configuration of the combination, to said axis; and

matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum speaker to deliver said sum signals thereto and connected to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms thereof move simultaneously in the same direction.

2. In an apparatus as set forth in claim 1, including:

top and bottom solid panel members extending forwardly from said front panel above and below said divider to the distal edge of said divider; and

a front solid panel member approximately centered on said distal edge and extending between said top and bottom members.

3. In a stereo-reproducing apparatus for use with a left channel signal and a right channel signal, the combination comprising:

a housing having an approximately vertical front panel board with a speaker opening therein;

a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately horizontal;

a divider mounted in front of said panel board and in juxtaposition thereto, said divider being substantially vertical, substantially normal to said panel board and coplanar with said axis, said divider having a pair of apertures therethrough;

a first difference speaker mounted on said divider in alignment with one aperture;

a second difference speaker mounted on said divider in alignment with the other aperture;

said difference speakers having diaphragms facing in opposite directions from each other, said difference speakers being positioned as closely adjacent as practical, considering the overall configuration of the combination, to said axis;

matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum speaker'to deliver said sum signals thereto and connected to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms thereof move simultaneously in the same direction; top and bottom solid panel members extending forwardly from said front panel above and below said divider to the distal edge of said divider; and a front solid panel member approximately centered on said distal edge and extending between said top and bottom members. 4. In an apparatus as set forth in claim 3, wherein said sum speaker has a diaphragm of a given width as measured horizontally across said axis, and said front solid panel member is at least equal to said given width as measured horizontally thereacross.

5. In a stereo-reproducing apparatus for use with a left channel signal and a right channel signal, the combination comprising:

a housing having an approximately horizontal front panel board with a speaker opening therein;

a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately vertical;

four difference speakers each having diaphragms defining respective axes, said difference speakers being mounted on said housing, in immediate juxtaposition to said opening and with their axes horizontal, one speaker of one pair of the difference speakers being oriented approximately 180 from the other speaker of said one pair, one speaker of the second pair of the difference speakers being oriented approximately 180 from the other speaker of said second pair, said one pair being oriented approximately 90 from said second pair; and

matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum speaker to deliver said sum signal thereto and connected to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms of one pair thereof move simultaneously in one direction and the diaphragms of the second pair thereof move simultaneously in another direction.

6. In an apparatus for use with a pair of amplifiers, each of which has a pair of terminals at which the respective left and right signals appear, said apparatus being in accordance with that set forth in claim 5 and wherein said matrixing means includes:

an autotransformer whose winding has two main connections separated by a centertap connection, said autotransformer having a relatively high impedance as compared to the speaker impedances;

said difference speakers being connected between said main connections;

means adapted to connect one main connection to one output terminal of one amplifier; means adapted to connect the other main connection to one output terminal of the other amplifier; and

means adapted to connect one side of the sum speaker to the other output terminals of the two amplifiers;

the other side of the sum speaker being connected to said center tap connection.

7. In an apparatus as set forth in claim 6, including:

divider means comprising four vertical wings positioned in the fonn of a Greek cross on the outside side of said panel board with the point of intersection of said cross on said axis, each of said wings having speaker openings therethrough;

said four difference speakers being mounted on a respective wing in alignment with the opening in the wing; and

an enclosure member extending across the distal edges of said wings.

8. In an apparatus as set forth in claim 5, including:

divider means comprising four vertical wings positioned in the form of a Greek cross onthe outside side of said panel board with the point of intersection of said cross on said axis, each of said wings having speaker openings therethrough;

said four difference speakers being mounted on a respective wing in alignment with the opening in the wing; and an enclosure member extending across the distal edges of said wings.

9. A matrixing device for use with a pair of amplifiers each of which has a pair of terminals with a left stereo signal appearing at the terminals of one amplifier and a right stereo signal appearing at the terminals of the other amplifier, and for use with a loudspeaker-reproducing system comprising sum speaker means and difierence speaker means, said device comprising:

an autotransformer whose winding has two main connections separated by a centertap connection, said autotransformer having a relatively high impedance as compared to the difference speaker means impedances;

said difference speaker means being connected only between said main connections;

means adapted to connect one main connection to one output terminal of one amplifier;

means adapted to connect the other main connection to one output terminal of the other amplifier; and

means adapted to connect one side of the sum speaker means to the other output terminals of the two amplifiers; the other side of the sum speaker means being connected to said center tap connection.

UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 3,637,938 lannaryLJfiL;

' Inv n Herbert rfxuhlow, James F. Novak. John F. Henlev It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Y

Substitute the following for Claim 1 of thepatent:

1. .In an apparatus for use with a pair of amplifiers, each of which has a pair of terminals at which the respective left and right signals appear, said apparatus v being for use with a left channel signal and a right 5 channel signal, the combination comprising:

a housing having an approximately vertical front panel board with a. speaker opening therein; a v

a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said l0 speaker having an axis. positionedapproximately horizontal;

a divider mounted in front of said panel board and injuxtaposition thereto, said divider being substantially vertical, substantially normal to said panel board and coplanar with. said axis, said divider having 'a pair of. l5 apertures therethrough;

a first difference speaker mounted on .said divider in alignment with one aperture Y v a second difference speaker mounted on said divider in alignment with the other aperture; 7

2O said difference speakers having diaphragms facing in opposite directions from each other, said difference speakers being positioned as closely'adjacent as practical, considering the overall configuration of the combination,

, to said axis; and

25 matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum 30 speaker to deliver said sum signals thereto and connected FORM (10-59)- USCOMM-DC sous-p69 U45. GOVERNMENT PRlNTING OFFICE: 965 0-356-334 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,637, 938 Dated January 25, 1972 Herbert F. 'Kuhlow, James F. Novak, John F. Henley It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

= 'to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms thereof move simultaneously in the same direction, said matrixing means including: 35' a an auto-transformer whose winding has two maineconnections separated by a center tap connection, said auto-transformer having a relatively high impedance as compared to the impedances of said difference speakers; I 40 said difference speakers being connected only between said main connections;

means adapted to connect one main connection. to one output terminal of one amplifier;

means adapted to connect the other main 45 connection to one output terminal of the other amplifier; and I means adapted to connect one side of the sum speaker to the otheroutput terminals of the two amplifiers; 50 v the other side of the sum speaker being connected to said center tap connection.

Signed and sealed this 17th day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT (FOTTSCHALK Attesting Officer I Commissioner of Patents F ORM PO-1050 (10-69) USCOMM-DC 6O376-P69 us, GOVERNMENT PRINTING OFFICE: I969 O3G6-334 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3,637,938 Januarv 25. 1972 Invent Herbert F. Kuhlow, James F. Novak. John F. Henlev It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

Substitute the following for Claim 1 of the patent:

l. vIn an apparatus for use with a pair of amplifiers, each of which has a pair of terminals at which the respective left and right signals appear, said apparatus being for use with a left channel signal and a right 5 channel signal, the combination comprising:

a housing having an approximately vertical fron panel board with a speaker opening therein;

a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately horizontal;

a divider mounted in front of said panel board and in juxtaposition thereto, said divider being substantially vertical, substantially normal to said panel board and coplanar with said axis, said divider having a pair of l5 apertures therethrough;

a first difference speaker mounted on said divider in alignment with one aperture;

a second difference speaker mounted on said divider in alignment with the other aperture; 7

said difference speakers having diaphragms facing in opposite directions from each other, said difference speakers being positioned as closely adjacent as practical, considering the overall configuration of the combination, to said axis; and

matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a. second output signal as the difference of said left and right signals, said means being connected to the sum speaker to deliver said sum signals thereto and connected FORM PO-O (10-69) USCOMM-DC 60376-F'69 [1.5, GOVERNMENT PRINTING OFFICE: I969 0-366-334 UNITED STATES PATENT FFICE CERTIFICATE OF CEQ'NGN Patent No. 3,637,938 D t January 25, 1972 Herbert F. 'Kuhlow, James F. Novak, John F. Henley It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

. 'to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms thereof move simultaneously in the same direction, said matrixing means including:

an auto-transformer whose winding has two main connections separated by a center tap connection, said auto-transformer having a relatively high impedance as compared to the impedances of said difference speakers; 40 said difference speakers being connected only between said main connections;

means adapted to connect one main connection. to one output terminal of one amplifier;

means adapted to connect the other main connection to one output terminal of the other amplifier; and

means adapted to connect one side of the sum speaker to the other output terminals of t the two amplifiers; the other side of the sum speaker being connected to said center tap connection.

Signed and sealed this 17th day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT QOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-O (10-69) USCOMM-DC 60376-P69 U.S, GOVERNMENT PRINTING OFFICE I969 O'366-334 

1. In a stereo-reproducing apparatus for use with a left channel signal and a right channel signal, the combination comprising: a housing having an approximately vertical front panel board with a speaker opening therein; a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately horizontal; a divider mounted in front of said panel board and in juxtaposition thereto, said divider being substantially vertical, substantially normal to said panelboard and coplanar with said axis, said divider having a pair of apertures therethrough; a first difference speaker mounted on said divider in alignment with one aperture; a second difference speaker mounted on said divider in alignment with the other aperture; said difference speakers having diaphragms facing in opposite directions from each other, said difference speakers being positioned as closely adjacent as practical, considering the overall configuration of the combination, to said axis; and matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum speaker to deliver said sum signals therEto and connected to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms thereof move simultaneously in the same direction.
 2. In an apparatus as set forth in claim 1, including: top and bottom solid panel members extending forwardly from said front panel above and below said divider to the distal edge of said divider; and a front solid panel member approximately centered on said distal edge and extending between said top and bottom members.
 3. In a stereo-reproducing apparatus for use with a left channel signal and a right channel signal, the combination comprising: a housing having an approximately vertical front panel board with a speaker opening therein; a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately horizontal; a divider mounted in front of said panel board and in juxtaposition thereto, said divider being substantially vertical, substantially normal to said panel board and coplanar with said axis, said divider having a pair of apertures therethrough; a first difference speaker mounted on said divider in alignment with one aperture; a second difference speaker mounted on said divider in alignment with the other aperture; said difference speakers having diaphragms facing in opposite directions from each other, said difference speakers being positioned as closely adjacent as practical, considering the overall configuration of the combination, to said axis; matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum speaker to deliver said sum signals thereto and connected to said difference speakers to deliver the difference signal thereto, the connection to the difference speakers being such that the diaphragms thereof move simultaneously in the same direction; top and bottom solid panel members extending forwardly from said front panel above and below said divider to the distal edge of said divider; and a front solid panel member approximately centered on said distal edge and extending between said top and bottom members.
 4. In an apparatus as set forth in claim 3, wherein said sum speaker has a diaphragm of a given width as measured horizontally across said axis, and said front solid panel member is at least equal to said given width as measured horizontally thereacross.
 5. In a stereo-reproducing apparatus for use with a left channel signal and a right channel signal, the combination comprising: a housing having an approximately horizontal front panel board with a speaker opening therein; a single sum speaker mounted in said housing and on said panel board in alignment with said opening, said speaker having an axis positioned approximately vertical; four difference speakers each having diaphragms defining respective axes, said difference speakers being mounted on said housing, in immediate juxtaposition to said opening and with their axes horizontal, one speaker of one pair of the difference speakers being oriented approximately 180* from the other speaker of said one pair, one speaker of the second pair of the difference speakers being oriented approximately 180* from the other speaker of said second pair, said one pair being oriented approximately 90* from said second pair; and matrixing means adapted to be connected to receive said signals for producing a first output signal as the sum of said left and right signals and for producing a second output signal as the difference of said left and right signals, said means being connected to the sum speaker to deliver said sum signal thereto and connected to said difference speakers to deliver the diFference signal thereto, the connection to the difference speakers being such that the diaphragms of one pair thereof move simultaneously in one direction and the diaphragms of the second pair thereof move simultaneously in another direction.
 6. In an apparatus for use with a pair of amplifiers, each of which has a pair of terminals at which the respective left and right signals appear, said apparatus being in accordance with that set forth in claim 5 and wherein said matrixing means includes: an autotransformer whose winding has two main connections separated by a centertap connection, said autotransformer having a relatively high impedance as compared to the speaker impedances; said difference speakers being connected between said main connections; means adapted to connect one main connection to one output terminal of one amplifier; means adapted to connect the other main connection to one output terminal of the other amplifier; and means adapted to connect one side of the sum speaker to the other output terminals of the two amplifiers; the other side of the sum speaker being connected to said center tap connection.
 7. In an apparatus as set forth in claim 6, including: divider means comprising four vertical wings positioned in the form of a Greek cross on the outside side of said panel board with the point of intersection of said cross on said axis, each of said wings having speaker openings therethrough; said four difference speakers being mounted on a respective wing in alignment with the opening in the wing; and an enclosure member extending across the distal edges of said wings.
 8. In an apparatus as set forth in claim 5, including: divider means comprising four vertical wings positioned in the form of a Greek cross on the outside side of said panel board with the point of intersection of said cross on said axis, each of said wings having speaker openings therethrough; said four difference speakers being mounted on a respective wing in alignment with the opening in the wing; and an enclosure member extending across the distal edges of said wings.
 9. A matrixing device for use with a pair of amplifiers each of which has a pair of terminals with a left stereo signal appearing at the terminals of one amplifier and a right stereo signal appearing at the terminals of the other amplifier, and for use with a loudspeaker-reproducing system comprising sum speaker means and difference speaker means, said device comprising: an autotransformer whose winding has two main connections separated by a centertap connection, said autotransformer having a relatively high impedance as compared to the difference speaker means impedances; said difference speaker means being connected only between said main connections; means adapted to connect one main connection to one output terminal of one amplifier; means adapted to connect the other main connection to one output terminal of the other amplifier; and means adapted to connect one side of the sum speaker means to the other output terminals of the two amplifiers; the other side of the sum speaker means being connected to said center tap connection. 